Porting one game's maps to another is illegal. (even though it seems like it is just an update to the same game) That is why you don't play on those 1.6 maps right now. They have to be revamped or reduxed or however the kids say it these days.

If you want to make a 1.6 map into source so badly then make it again, if that's too much work then get someone else to do it for you.

its illegal because a lot of game company do not allowed their things to get into other games such as css to 1.6 and such but on some game they allowed it such as stalker. so thats it. no porting what so ever here

He's most likely NOT talking about an official map...

Find the maps you'd like to be remade and see if the original creator will re-make them.

If not, ask them for permission to remake them.

Or you can by-pass copyrights and make it 10% different from the original. ;)

Heh, screw the copyright.. I think you can recompile the maps, all ya' need is the will to do it.

Its very easy but its ILLEGAL and alot of stuff get fucked up.. so i wouldnt recommend it. just remake it

Indeed, lots of entities are different in the Goldsource engine compared to source. Also you would have tones of invalid brushes. My advice, redo it from scratch on the Source engine. It would also be a good idea to improve the quality and detail this way.